breathable steel – Researchers outline how “breathable” steel can be produced using selective laser melting (SLM) by mixing a foaming agent into steel powder. The approach creates interconnected pores on the order of 80 micrometers or less, letting gases vent through steel molds
Imagine building a mold meant to survive high temperatures and crushing pressures—only to discover the real enemy isn’t the plastic. It’s the air.
In injection molding. steel is the go-to material for tooling because it’s hard. resilient. and easy to machine into precise geometry.. But steel doesn’t “breathe.” It’s solid and impermeable. so when hot plastic is injected. the air inside the mold has nowhere to go.. If it can’t escape fast enough, the gas ends up dissolved in the molten plastic.. The result is familiar to casting engineers: voids, surface imperfections, and other irregularities.. Chasing those defects in finished parts becomes an endless battle against heat transfer and fluid mechanics.
Traditionally. teams reduce the damage by redesigning the mold itself—adding exhaust ports or vacuum hookups so air can vent out.. That can work, but it also demands a lot of careful engineering to keep defect rates low during mass production.. Miss the timing. miss the venting path. or trap gas in the wrong corner. and the mold goes back to the drawing board.
Breathable mold steel flips the problem.. Instead of relying on ports and vacuum connections, it aims to vent gas through the tooling material itself.. The idea is to create a steel mold with tiny pores that allow air to pass through while remaining largely impermeable to the molten plastic being molded.
Making that work is far from straightforward.. The article’s approach centers on selective laser melting (SLM) 3D printing. which uses a high-powered laser to fuse metal powder together layer by layer into a final part.. The key move is combining a foaming agent with the powder so that. as the part forms. the decomposition of that foaming agent generates gas bubbles that become pores.
In the described research. breathable steel is produced via SLM by mixing a foaming agent into steel powder to generate interconnected micrometer-scale pores.. The pores must be small—around 80 micrometers or less—so gas in the mold can pass freely while blocking the flow of larger polymer molecules in the injected plastic.
Chromium nitride is one foaming agent mentioned.. It releases both chromium (Cr) and nitrogen (N) during decomposition. and those released elements are described as lending beneficial properties to the steel of the finished product.. The foaming agent is mixed into the steel powder, then melts along with it as the part is being produced.. As the foaming agent breaks down, gas bubbles form pores in a way that the paper says is relatively predictable.
The level of porosity isn’t fixed.. It can be controlled by how much foaming agent is mixed in and by the laser settings.. Lower melt pool temperatures—driven by faster scanning speeds or lower laser powers—tend to favor more porous structures.. The reasoning is tied to fluid mechanics: cooler liquid steel flows into existing pores differently than hotter melts.
This isn’t the first attempt to make molds vent through metal.. The article notes earlier efforts using premade breathable steel inserts: rectangular inserts or round bars made from “ventilated steel” such as PM-35.. That material is created by sintering steel powders to reach a porosity of 20–30%.. But the process isn’t always well suited for advanced injection mold geometry.. The constraints show up again when the method is narrowed to local inserts—creating breathable rods and bars that act as localized vents rather than making the entire mold out of breathable steel.
Other powder metal techniques can produce complex vented parts, but they can be expensive and difficult to execute well down to smaller pore sizes. The SLM route, with an additional foaming agent, is presented as simpler—especially for smaller pores.
The piece also points out that the SLM-based approach has shown more admirable mechanical properties in some cases compared with PM-35 steel, including impressive compressive strength as well as hardness and corrosion resistance.
For most people, breathable steel won’t show up in daily life.. It’s aimed at specialized manufacturing contexts—particularly if someone already has expensive 3D printing hardware for metal powders and wants a complex metal part that’s also porous.. Still. the appeal is hard to miss: turning steel. a material typically treated as impermeable by default. into something that can let gas move through it.. In injection molding. where trapped air can sabotage quality. that shift—from ports and vacuum hookups to pores inside the steel itself—could change how molds are designed and how often defects force a reset.
breathable steel injection molding selective laser melting SLM foaming agent chromium nitride chromium nitride decomposition porous steel casting defects metal 3D printing PM-35 micrometer pores
So it’s like a sponge steel mold? Cool I guess.
Wait so they put a foaming agent in the steel powder? And it somehow lets gas out but not molten plastic… seems kinda backwards to me. Injection molding is already messy enough.
Breathable steel sounds like they’re basically trying to make steel porous like bread. But if the pores are like 80 micrometers, wouldn’t that clog up the second the plastic touches it? Also I read “SLM” and thought it was some new battery thing lol.
This reminds me of how air bubbles ruin stuff when you’re using resin or something. They keep saying ‘air is the enemy’ but isn’t it always heat and pressure? Like if you just vent the mold better you don’t need “breathable” steel. Unless they’re saying the ports fail in mass production or whatever.